An ion beam is a type of particle beam consisting
of ions.
Ion beams have many uses in electronics
manufacturing (principally ion implantation) and
other industries.
Principle
Of
IBM
Three types of collision between ion and atom
Effects of low and high energies on atom removal
(a) low energy case (b) high energy case
IBM System
An ion beam machine:
A plasma source which generates the tons Extraction grids for removing the ions from the plasma, and accelerating them towards the substrate (or specimen)
Main Components of ion beam machine
• The Ion Source has arrays of permanent magnets to produce a multi-cusp magnetic field in regions remote from the plasma grid and the RF antenna.
• The field confines the plasma by lengthening the path of ionizing electrons and reducing their drift to the walls.
• Plasma sources generate plasmas.
• Excitation of plasma requires partial ionization of neutral atoms and/or molecules of a medium.
• There are several ways to cause ionization: collisions of energetic particles, strong electric fields acting on bond electrons, or ionizing radiation.
- The following reaction occurs:
• Argon ions are thereby produced.
• A magnetic field, obtained from an electromagnetic coil or a permanent magnet, is often applied between the anode and cathode to make the electrons spiral.
• Spiraling increases the path length of the electrons and hence increases ionization.
e
Ar
e
Ar
2
IBM System
• The ions are removed from the plasma by means of extraction grids.
• The grids are normally made of two or three arrays of perforated sheets of carbon or molybdenum; these
materials can withstand erosion by ion bombardment. • The perforations in each of the sheets are aligned
above one another.
- The outer grid
• The outer grid is usually kept at ground potential, which is a more negative level than that of the anode.
• This grid therefore provides the negative field that is needed to remove the ions from the plasma.
IBM System
- The second grid
The second grid is held at a negative potential below the ground value.
The escape of electrons from the plasma is thereby prevented, as is their diffusion back from the work chamber.
- A third grid
• A third grid, which is maintained at the anode potential, is sometimes added placed between the plasma and the
electron suppressor grid to improve the performance of the source.
IBM System
- Ground Electrodes
Ground Electrodes are used for extracting positively
charged ions from the source that combine downstream to form a broad beam.
Individual electrodes in close proximity to the extraction electrode can be biased to inhibit back streaming of
neutralizing中和 electrons close to the source or back to the extraction electrode.
• Output voltages and currents are precisely controlled from the front panel or by remote programming.
• Digital displays on the front panel directly monitor the voltage and current outputs.
• Remote analog signals proportional to each output are provided at the rear panel I/O connector.
• Focusing of the Ion Beam is also provided by the construction and shape of the electrodes.
• The suppression electrode produces an inner zero electrostatic field, and an outer electrostatic on a field such that ions
entering this outer field are deflected by an amount that is a function of their distance from the edge of the inner field.
• The result is a focused beam having a uniform intensity over a given target area and at a given distance from the lens.
• Ion beams can be used for sputtering or ion beam etching and for ion beam analysis.
• Ion beam etching, or sputtering, is a technique conceptually similar to sandblasting, but using individual atoms in an ion beam to ablate a target.
• Reactive ion etching is an important extension that uses
chemical reactivity to enhance the physical sputtering effect.
Applications of IBM
• In a typical use in semiconductor manufacturing, a mask is used to selectively expose a layer of photoresist on a substrate such as a silicon dioxide or gallium arsenide wafer.
• The wafer is developed, and for a positive photoresist, the exposed portions are removed in a chemical process.
• The result is a pattern left on the surface areas of the wafer that had been masked from exposure.
• The wafer is then placed in a vacuum chamber, and exposed to the ion beam.
• The impact of the ions erodes the target, abrading away the areas not covered by the photoresist.
• This method is frequently enhanced by bleeding a reactive gas into the vacuum system, which is known as reactive ion etching.
Applications of IBM
Focused Ion Beam (FIB) instruments are also used in the design verification and/or failure analysis of semiconductor devices.
Engineering prototype devices may be modified using the ion beam in order to rewire the
electrical circuit.
The technique may be effectively used to avoid performing a new mask run for the purpose of testing design changes.
A device edit (FIB milling operation) is accomplished by focusing the ion beam on selected regions of the device in order to mill through metal or polysilicon structures.
Applications of IBM
Sputtering is also used in materials science to thin
samples or specific regions of samples for transmission electron microscope analysis, or for extending surface analytical techniques such as secondary ion mass
spectrometry or electron spectroscopy (XPS, AES) so that they can depth profile them.
Applications of IBM
- Ion-beam Etching - Ion-beam sputtering - Ion-beam sculpting - Basis
- Broad area ion exposure - TEM exposure - Smoothing - Texturing - Cleaning - Shaping,Polishing, Thinning - Milling
Applications
• Removing atoms by sputtering with an inert gas is called ‘ion milling’ or ‘ion etching’.
• Sputtering can also play a role in reactive ion etching
(RIE), a plasma process carried out with chemically active ions and radicals, for which the sputtering yield may be enhanced significantly compared to pure physical
sputtering.
Applications of IBM
Ion-beam sputtering (IBS) is a method in which the target is external to the ion source.
A source can work without any magnetic field like in a Hot filament ionization gauge . In a Kaufman source ions are generated by
collisions with electrons that are confined by a magnetic field as in a magnetron.
They are then accelerated by the electric field emanating from a grid toward a target.
• Ion-Beam sculpting is a term used to describe a two-step process to make solid-state nanopores.
• The term itself was coined by Golovchenko and co-workers at Harvard in the paper "Ion-beam sculpting at nanometer length scales".
• The term refers to the fact that solid-state nanopores are formed by lateral mass transport about the surface of the
substrate, not simply by sputtering which refers to the removal of material from the surface.
• The first step in ion sculpting is to make either a through hole or a blind hole, most commonly using an focused ion beam (FIB).
• The holes are commonly ~100nm, but can be made much smaller.
• This step may or may not be done at room temperature, with a low temperature of -120℃.
• Next, there are three common techniques to now 'sculpt' the hole: broad area ion exposure, TEM exposure, and FIB exposure. Holes can be closed completely, but also they can be left open at a lower limit of 1-10nm.
• This technique uses a broad area argon ion source beam. • If the hole is blind，the wafer (often SiN or silicon oxide) is
then turned upside down, and exposed with the argon beam. • A detector counts the amount of ions passing through the
membrane (which should be zero).
• The process stops when ions begin to be detected.
Applications of IBM
• A through hole in a wafer can be closed down by a transmission electron microscope.
• Due to hydrocarbon buildup, the electrons stimulate hole closure.
• This method is very slow (taking over an hour to close a 100 nm hole).
• The slow method allows for great control of the hole size
(since you can watch the hole decrease), but its drawback is that it takes a long time.
• The use of IBM for smoothing of laser mirrors and for modifying the thickness of thin films and membranes without affecting surface finish is reported by Jolly, and Reader.
• Hudson has demonstrated that an ion-beam source is a controlled method for texturing surfaces.
• A typical result is presented which a structure resembling closely packed cones was produced.
• As well as the nickel and copper, Hudson went on to investigate 26 materials, including stainless steel, silver and gold.
• Atomically clean surfaces can be produced by IBM. • This technique can be preferable to electron beam and
electrical discharge methods which can damage the surface.
• Harper, Cuomo and Kaufman discuss in detail this well-established application of ion beam technology.
• Thinning by use of oblique incidence argon ions has been used to enhance polishing.
• Macroscopic thinning and shaping of materials can be applied to the fabrication of magnetic heads and surface acoustic wave devices.
IBM of aspheric lens
Applications of IBM
Shapening of diamong
indenter by IBM
Sharpening of diamond
microtome cutter
Manufacture of holographic mask
Production of magnetic
bubble memory
Ion milling of
permalloy structure
Applications of IBM
• Ion milling is especially useful for the accurate production of shallow grooves.
• Milling through masks to produce regular arrays of pits with widths of 5 to 200μm and depths of up to 1mm for enhanced bonding.
• Pillar-like configurations useful in the manufacture of precision electrical resistive and fiber optic arrays can be produced by ion beam methods.
Showing the ability of ion milling to etch near-vertical walls
A Ni-Fe bar bubble memory pattern
Narrow line widths produced
in carbon membrane by IBM
• Ion implantation is a material engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties of the solid.
• Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in materials science research.
• Ion implantation equipment typically consists of an ion source, where ions of the desired element are produced, an
accelerator, where the ions are electrostatically accelerated to a high energy, and a target chamber, where the ions impinge on a target, which is the material to be implanted.
• Typical ion energies are in the range of 10 to 500keV. • Energies in the range 1 to 10keV can be used, but result
in a penetration of only a few nanometers or less.
• Energies lower than this result in very little damage to the target, and fall under the designation ion beam deposition. • Higher energies can also be used: accelerators capable of
5MeV are common.
• The energy of the ions, as well as the ion species and the composition of the target determine the depth of penetration of the ions in the solid:
a) A mono-energetic ion beam will generally have a broad depth distribution.
b) The average penetration depth is called the range of the ions. c) Under typical circumstances ion ranges will be between 10
nanometers and 1 micrometer.
Application of Ion
implantation
- Doping
- Silicon on Insulator - Mesotaxy
- Tool steel toughening - Surface finishing - Crystallographic - Amprphization - Damage recovery - Sputtering - Ion channeling - Hazardous Materials Note
- High Voltage Safety
• The introduction of dopants in a semiconductor is the most common application of ion implantation.
• Dopant ions such as boron, phosphorus or arsenic are
generally created from a gas source, so that the purity of the source can be very high.
• These gases tend to be very hazardous.
Application of Ion
implantation
• One prominent method for preparing silicon on insulator (SOI) substrates from conventional silicon substrates is the SIMOX process, wherein a buried high dose oxygen implant is converted to silicon oxide by a high
temperature annealing process.
Application of Ion
implantation
• Mesotaxy is the term for the growth of a crystallographically matching phase underneath the surface of the host crystal (compare to epitaxy, which is the growth of the matching phase on the surface of a substrate).
• In this process, ions are implanted at a high enough energy and dose into a material to create a layer of a second phase, and the temperature is controlled so that the crystal structure of the target is not destroyed.
Application of Ion
implantation
• Nitrogen or other ions can be implanted into a tool steel target. • The structural change caused by the implantation produces a
surface compression in the steel, which prevent crack
propagation and thus makes the material more resistant to fracture.
• The chemical change can also make the tool more resistant to corrosion.
Application of Ion
implantation
• Ion implantation is used in such cases to engineer the surfaces of such devices for more reliable performance.
• As in the case of tool steels, the surface modification caused by ion implantation includes both a surface compression
which prevents crack propagation and an alloying of the surface to make it more chemically resistant to corrosion.
Application of Ion
implantation
Vacancies and Interstitials.
• Vacancies are crystal lattice points unoccupied by an atom: in this case the ion collides with a target atom, resulting in
transfer of a significant amount of energy to the target atom such that it leaves its crystal site.
• Interstitials result when such atoms (or the original ion itself) come to rest in the solid, but find no vacant space in the
lattice to reside.
Application of Ion
implantation
• Because ion implantation causes damage to the crystal structure of the target which is often unwanted, ion
implantation processing is often followed by a thermal annealing.
• This can be referred to as damage recovery.
Application of Ion
• In some cases, complete amorphization of a target is preferable to a highly defective crystal.
• An amorphized film can be regrown at a lower temperature than required to anneal a highly damaged crystal.
Application of Ion
implantation
• Some of the collision events result in atoms being ejected (sputtered) from the surface, and thus ion implantation will slowly etch away a surface.
• The effect is only appreciable for very large doses.
Application of Ion
• If there is a crystallographic structure to the target and especially in semiconductor substrates where the crystal structure is more open, particular crystallographic directions offer much lower stopping than other directions.
• The result is that the range of an ion can be much longer if the ion travels exactly along a particular direction, for example the <110> direction in silicon and other diamond cubic materials. • This effect is called ion channeling.
Application of Ion
implantation
• The toxic materials used in the ion implanter process.
• Such hazardous elements, solid source and gasses are used, such as Arsine and Phosphine .
• Other elements may include Antimony, Arsenic, Phosphorus, and Boron.
• It is important not to expose yourself to these carcinogenic, corrosive, flammable, and toxic elements.
Application of Ion
implantation
• High voltage power supplies in ion implantation equipment can pose a risk of electrocution.
• In addition, high-energy atomic collisions can generate radionuclides.
• Prior to entry to high voltage area, terminal components must be grounded using a grounding stick.
Application of Ion
implantation
• Low temperature processing reduces handling an stress problems.
• No dimensional changes
• Good adhesion of treated surface • New alloys possible
• Can improve corrosion, oxidation, wear, hardness, friction, fatigue
• Very shallow treatment (< 1 μm) • High cost
• The surface can be weakened by radiation effects
Summary of IBM
• Nitrogen implantation has been used to increase wear resistance and give longer life,
• injection molding screws • high speed steel tools • a clutch housing tool • hip prosthesis
• Yttrium gives oxidation and wear resistance
• Titanium and carbon on iron gives lower friction and better wear.
• Chromium is used to maintain strength of holes.
